A variety of factors involved in the blood clotting process have been identified, including factor VII (FVII), a plasma glycoprotein. Haemostasis is initiated by the formation of a complex between tissue factor (TF) being exposed to the circulating blood following an injury to the vessel wall, and FVIIa which is present in the circulation in an amount corresponding to about 1% of the total FVII protein mass. FVII exists in plasma mainly as a single-chain zymogen, which is cleaved by FXa into its two-chain, activated form, FVIIa. Recombinant activated factor VIIa (rFVIIa) has been developed as a pro-haemostatic agent. The administration of rFVIIa offers a rapid and highly effective pro-haemostatic response in haemophilic subjects with bleedings who cannot be treated with other coagulation factor products due to antibody formation. Also bleeding in subjects with factor VII deficiency or subjects having a normal coagulation system but experiencing excessive bleeding can be treated successfully with FVIIa.
It is desirable to have administration forms of factor VIIa suitable for both storage and for delivery. Ideally, the drug product is stored and administered as a liquid. Alternatively, the drug product is lyophilized, i.e., freeze-dried, and then reconstituted by adding a suitable diluent just prior to patient use. Ideally, the drug product has sufficient stability to be kept in long-term storage, i.e., more than six months.
The decision to either maintain the finished drug product as a liquid or to freeze-dry it is usually based on the stability of the protein drug in those forms. Protein stability can be affected inter alia by such factors as ionic strength, pH, temperature, repeated cycles of freeze/thaw, and exposures to shear forces. Active protein may be lost as a result of physical instabilities, including denaturation and aggregation (both soluble and insoluble aggregate formation), as well as chemical instabilities, including, for example, hydrolysis, deamidation, and oxidation, to name just a few. For a general review of stability of protein pharmaceuticals, see, for example, Manning, et al., Pharmaceutical Research 6:903-918 (1989).
While the possible occurrence of protein instabilities is widely appreciated, it is impossible to predict particular instability problems of a particular protein. Any of these instabilities can result in the formation of a protein by-product, or derivative, having lowered activity, increased toxicity, and/or increased immunogenicity. Indeed, protein precipitation may lead to thrombosis, non-homogeneity of dosage form and amount, as well as clogged syringes. Furthermore, posttranslational modifications such as, for example, gamma carboxylation of certain glutamic acid residues in the N-terminus and addition of carbohydrate side chains provide potential sites that may be susceptible to modification upon storage. Also, specific to factor VIIa, being a serine protease, fragmentation due to autocatalysis may occur (enzymatic degradation). Thus, the safety and efficacy of any composition of a protein is directly related to its stability. Maintaining stability in a liquid form is generally different from a lyophilized form because of greatly increased potential for molecular motion and therefore increased probability of molecular interactions. Maintaining stability in a concentrated form is also different because of the propensity for aggregate formation at increased protein concentrations.
When developing a liquid composition, many factors are taken into consideration. Short-term, i.e., less than six months, liquid stability generally depends on avoiding gross structural changes, such as denaturation and aggregation. These processes are described in the literature for a number of proteins, and many examples of stabilizing agents exist. It is well known that an agent effective at stabilizing one protein actually acts to destabilize another. Once the protein has been stabilized against gross structural changes, developing a liquid composition for long-term stability (e.g., greater than six months) depends on further stabilizing the protein from types of degradation specific to that protein. More specific types of degradation may include, for example, disulfide bond scrambling, oxidation of certain residues, deamidation, cyclization. Although it is not always possible to pinpoint the individual degradation species, assays are developed to monitor subtle changes so as to monitor the ability of specific excipients to uniquely stabilize the protein of interest.
In addition to stability considerations, one generally selects excipients, which are approved by various worldwide medical regulatory agencies. It is desirable that the pH of the composition is in a physiologically suitable range upon injection/infusion, otherwise pain and discomfort for the patient may result.
For a general review of protein compositions, see, for example, Cleland et al.: The development of stable protein compositions: A closer look at protein aggregation, deamidation and oxidation, Critical Reviews in Therapeutic Drug Carrier Systems 1993, 10(4): 307-377; and Wang et al., Parenteral compositions of proteins and peptides: Stability and stabilizers, Journal of Parenteral Science and Technology 1988 (Supplement), 42 (2S).
Other publications of interest regarding stabilization of proteins are as follows.
U.S. 20010031721 A1 (American Home Products) concerns highly concentrated, lyophilised, and liquid factor IX compositions.
U.S. Pat. No. 5,770,700 (Genetics Institute) concerns liquid factor IX compositions.
WO 97/19687 (American Red Cross) concerns liquid compositions of plasma proteins, in particular factor VIII and factor IX.
U.S. Pat. No. 4,297,344 discloses stabilization of coagulation factors II and VIII, antithrombin III, and plasminogen against heat by adding selected amino acids such as glycine, alanine, hydroxyproline, glutamine, and aminobutyric acid, and a carbohydrate such as a monosaccharide, an oligosaccharide, or a sugar alcohol.
Factor VIIa undergoes several degradative pathways, especially aggregation (dimerisation), oxidation, and autolytic cleavage (clipping of the peptide backbone). Furthermore, precipitation may occur. Many of these reactions can be slowed significantly by removal of water from the protein. However, the development of an aqueous composition for factor VIIa has the advantages of eliminating reconstitution errors, thereby increasing dosing accuracy, as well as simplifying the use of the product clinically, thereby increasing patient compliance. Ideally, compositions of factor VIIa should be stable for more than 6 months over a wide range of protein concentrations. This allows for flexibility in methods of administration. Generally, more highly concentrated forms allow for the administration of lower volumes, which is highly desirable from the patients' point of view. Liquid compositions can have many advantages over freeze-dried products with regard to ease of administration and use.
Today, the only commercially available, recombinantly-made FVII polypeptide composition is a freeze-dried factor FVIIa product which is reconstituted before use; it contains a relatively low factor VIIa concentration, e.g., about 0.6 mg/ml. A vial (1.2 mg) of NovoSeven® (Novo Nordisk A/S, Denmark) contains 1.2 mg recombinant human factor VIIa, 5.84 mg NaCl, 2.94 mg CaCl2, 2 H2O, 2.64 mg GlyGly, 0.14 mg polysorbate 80, and 60.0 mg mannitol; it is reconstituted to pH 5.5 by 2.0 ml water for injection (WFI). When reconstituted, the protein solution is stable for use for 24 hours. Thus, no liquid ready-for use- or concentrated factor VII products are currently commercially available.
Accordingly, there is a need in the art for methods for improving stability of factor VII polypeptides, including human factor VIIa (chemical and/or physical stability), increasing the concentration, maintaining activity levels, and providing liquid compositions suitable for storage. Thus, it is an objective of this invention to provide an aqueous factor VII polypeptide composition which provides acceptable control of chemical and/or physical degradation products such as enzymatic degradation or autocatalysis products.